An electrospinning process is attracting attention as a technique that allows for relatively easy production of nano-diameter fiber (i.e., nanofiber) without using a mechanical or thermal force. A conventional Electrospinning process includes loading a solution of a nanofiber material into a syringe having a needle at its tip and jetting the solution from the needle toward a facing collecting electrode while applying a high direct voltage between the needle and the collecting electrode. The solvent of the jetted solution evaporates instantaneously, and the material is drawn by the coulomb force while coagulating into a nanofiber, which deposits on the collecting electrode.
The above described conventional electrospinning process is capable of producing only one or a few nanofibers from one needle. A technology for quantity production of nanofibers has not yet been established, and practical application of the electrospinning process has made only slow progress.
With the object of increasing the productivity in nanofiber manufacturing, Patent Literature 1 below discloses a method for producing nanofiber including providing a plurality of electrospinning devices arranged in parallel with one another and a nanofiber collector. The devices each include: a small-diametered metallic ball; a metallic spinning nozzle which is placed in such a manner that a distance between the metallic ball and the opening of the spinning nozzle is reduced; and a high speed air jet nozzle which is configured to direct a high speed air jet perpendicular to the line connecting the metallic ball and the opening of the spinning nozzle. A high voltage is applied between the metallic ball and the spinning nozzle to make a nanofiber, and the nanofibers spun from the nozzles are gathered and collected on the collector.
Patent Literature 2 below discloses an apparatus for nanofiber production including: a jet spinning nozzle grounded through selected one of two rectifiers; a dielectric composed of an electrode having, thereon, a dielectric insulating covering and a conducting covering; and an alternating-current source for applying AC current to the dielectric. The polarity of the charge of the spinning nozzle as grounded is reversed alternately so that nanofibers of opposite polarities are produced alternately, thereby to prevent the atmosphere from being charged to a single polarity. This allows for simplifying the system for insulation and safety of the production apparatus, and nearby members are prevented from being charged, making nanofiber collection easier.
Patent Literature 3 below discloses an apparatus for nanofiber production having, in place of a spinning nozzle, a conductive cylinder having a diameter of 10 mm to 300 mm and a large number of orifices through its wall. A voltage is applied between the cylinder and an electrode having an insulating covering on its side facing the cylinder to form nanofibers, which are attracted by two collector electrodes (attracting electrodes) having opposite polarities and deposited on a collector. The insulating covering, being as thin as 0.2 mm, protects the electrode from adhesion of the nanofibers and changes the charged state of the nanofibers, and the nanofibers are collected efficiently by using two collector electrodes (attracting electrodes).
Patent Literature 4 proposes using a resin-made jet spinning nozzle instead of a metallic nozzle. By the use of a resin-made nozzle, the solidification of the spinning solution at the nozzle is made controllable, which makes the nozzle cleaning operation easier and prevents a discharge from the nozzle. According to this technique, the spinning solution is charged by placing an electrode of whatever shape in the container containing the stock spinning solution or in the path between the container and the nozzle.